Degradation efficiency and mechanism of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) by thermally activated persulfate system

Polybrominated diphenyl ethers (PBDEs) as a typical brominated flame retardant (BFR) have attracted worldwide attention due to the high environmental risk and resistance to conventional remediation processes. In this study, thermally activated persulfate (TAP) process was applied to degrade 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), which is the most toxic and representative PBDEs in e-waste dismantling sites. Impact factors such as PDS dosage, heating temperature, and initial pH were evaluated. Results showed that BDE-47 can be 100% degraded within 180 min under the condition of PDS:BDE-47 = 1000:1, 60 degrees C, and pH = 7. Quenching experiments combined with EPR analysis further proved the important role of SO4 center dot- in oxidating BDE-47. According to high-resolution mass spectrometry (HRMS) analysis, only one oxidation product of low toxicity was detected during the oxidation process. Theoretical calculations further revealed that the oxidation process mainly involved radical attack at C-Br bond, cleavage of C-Br bond, and fission of ether bond, and HSO4 center dot may also play an important role in BDE-47 degradation in TAP system. In addition, TAP system exhibited universality as all selected PBDE congeners can be degraded, and the degradation rate of PBDEs was greatly affected by the number of substituted Br atoms in a negative trend. Overall, these findings indicate that TAP can be applied as an effective method for removal of PBDEs, and we provide a new insight for the practical application of TAP technology in BDE-47 degradation from experimental and theoretical aspects.

Automated summary

In this study, the thermally activated persulfate (TAP) process was used to degrade the most toxic and representative polybrominated diphenyl ethers (PBDEs) in e-waste dismantling sites. The results showed that 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) can be completely degraded under specific conditions, and only one oxidation product of low toxicity was detected. The TAP system exhibited universality for degrading PBDEs and the degradation rate was influenced by the number of substituted bromine atoms.